1. Field of the Invention
The present invention relates to a device for transferring paper sheets in a printing device, a copying device, etc., and more particularly, to a paper sheet transfer device having a paper sheet separating function so as to transfer paper sheets one by one successively in separation.
1. Description of the Prior Art
It is conventionally know to incorporate such a paper sheet transfer device having a paper sheet separating function in a printing device, a copying device, etc., so as to transfer paper sheets one by one successively in separation, that comprises a paper sheet feed roller adapted to be driven for rotation, and a press member disposed to oppose a cylindrical outer surface of the paper sheet feed roller along a generatrix thereof so as to define a nip region therebetween for nipping a paper sheet therein, wherein the friction coefficient between the outer surface of the paper sheet feed roller and a first surface of the paper sheet to contact therewith is higher than a friction coefficient between the first surface of the paper sheet and a second surface of the paper sheet opposite to the first surface, and the friction coefficient between a band surface area of the press member opposing the paper sheet feed roller in the nip region and the second surface of the paper sheet is lower than the friction coefficient between the outer surface of the paper sheet feed roller and the first surface of the paper sheet but higher than the friction coefficient between the first and second surfaces of the paper sheet, so that, when the paper sheet feed roller is driven for rotation, the paper sheets fed to the nip region is transferred through the nip region one by one successively in separation.
The paper sheet transfer device of the above-mentioned construction can be operated in such a manner that the paper sheets are transferred one by one successively in separation generally without fail, when the friction coefficient between the outer surface of the paper sheet feed roller and the first surface of the paper sheet and the friction coefficient between the band surface area of the press member and the second surface of the paper sheet are properly determined in relation to the friction coefficient between the first and second surfaces of the paper sheet.
However, when the friction characteristic of the first surface and/or the second surface of the paper sheet varies according to changes of the kinds of the paper sheets to be processed, the conventional paper sheet transfer device of this type is put into such troubles that the separation of the paper sheets becomes insufficient or the transfer of the paper sheets becomes insufficient. In more detail, when the friction coefficient between the first and second surfaces of the paper sheet becomes higher than an expected design value, the separation of the paper sheets becomes insufficient so that two or more paper sheets are often transferred together through the nip region as overlapped one over another. This is due to the insufficiency of the friction coefficient between the press member and the second surface of the paper sheet relative to the friction coefficient between the first and second surfaces of the paper sheet. On the other hand, when the friction coefficient between the first and second surfaces of the paper sheet becomes lower than an expected design value, although no malfunction occurs with respect to the separation of the paper sheets, if the decrease of the friction coefficient between the first and second surfaces of the paper sheet is due to a decrease of the friction characteristic of at least the first surface of the paper sheet, the transfer of the paper sheets becomes uncertain.